A virus scan process for detecting a computer virus-infected file and repairing or removing this file places a relatively large load on a computer system. However, as disclosed in U.S. Pat. No. 6,477,544, a system for accessing a Link File comprising links to a Common Store File and differences with the Common Store File (dirty portions) is known (Patent Literature 1). In this prior art, a virus scan is not performed for the Common Store File even when a scan is performed for a file accessed by a user in accordance with an access trigger.
Alternatively, to lessen the load generated by a virus scan process, a technology for storing the results of previous virus scan processes and only performing a virus scan process on a file, which was updated subsequent to the last scan, has been proposed (Patent Literature 2). In addition, a technology for identifying an updated file based in an updated block, and performing a virus scan process only for this updated file when creating a multi-generation backup has also been proposed (Patent Literature 3).